1. Field of the Invention
This invention relates to telecommunications. Specifically, the present invention relates to a system and method of providing a conversion between time-division multiplexed digital signals and packetized digital signals with a switching system interface utilized to bypass a common control and switch matrix of a digital switch.
2. Description of the Related Art
A class 5 central office comprises a building or room which houses a class 5 switching system, which operates to connect telephones and other devices used by end-user customers (“subscribers”) to a telecommunications network such as the public switched telephone network (“PSTN”). A class 5 digital switch also converts the analog signals used by telephones, modems, FAX machines, and some PBX trunks, into the digital signals that are routed through a digital telecommunications network. The class 5 digital switch also provides special services for caller ID displays and message waiting lights for subscribers, and it processes and routes calls from digital PBX trunks, ISDN lines, and digital loop carriers (“DLC”) to a telecommunications network.
U.S. Pat. No. 6,807,273 (“'273”) discloses a novel method and system for bypassing a common control and switch matrix of a class 5 digital switch by a switching system interface that couples one or more line/trunk frames of the digital switch to one or more transmission facilities in a communications network that preferably operates under an industry-recognized protocol.
A common control and switch matrix of a first class 5 digital switch may be bypassed by a switching system interface that couples one or more line/trunk frames of the digital switch to one or more industry standard digital transmission facilities that make up the remote end of an industry standard DLC architecture. This configuration provides the benefit that the line/trunk frames associated with the first digital switch may be operated by a second class 5 digital switch or media gateway of any manufacture, so that the legacy software of the first digital switch may be discarded and/or any limitations of the legacy switch matrix may be overcome, while retaining the installed legacy line/trunk frames and cable plant and incurring minimal changes to the installed physical plant.
There is a trend to employ networks that carry both voice calls and data over common transport based on connectionless access protocols such as asynchronous transfer mode (“ATM”) and transport control protocol/internet protocol (“TCP/IP”). These networks are also referred to as “packet networks”. Packet networks simplify the problem of carrying both voice and data from region to region. Routing calls over such a network permits the use of common routing hardware controlled by so-called “soft switches”, which essentially are computers running call processing software.
“Media gateways” are specialized packet switches that also convert the time-division multiplexed digital format of voice calls on trunks from legacy class 5 switches into the packetized formats used in packet networks. Present methods require the use of a media gateway in order to route calls from legacy time-division multiplexed equipment through a packet network.
Virtually all media gateways support GR303 as a protocol for interfacing to time-division multiplexed equipment. Therefore, a switching system interface for bypassing the common control and switch matrix of a class 5 digital switch, by coupling the line/trunk frames of the digital switch to digital transmission facilities that make up the remote end of an industry standard DLC architecture, can be used with a media gateway to route calls between the line/trunk frames and a packet network. However, the cost and complexity are increased by virtue of the fact that two types of network equipment must be purchased, installed, and administered. The complexity of this configuration may be further increased if the softswitch that processes calls for the packet network controls both the media gateway and switching system interface.
Therefore, what is needed is a system and method to provide the conversion between time-division multiplexed digital signals and packetized digital signals within the switching system interface in order to eliminate separate and different types of costly equipment, such as media gateways.
If a network operator chooses to bypass the common control and switch matrix of several class 5 digital switches, one or more of the line/trunk frames of each of the digital switches may be placed under the control of another digital switch that provides call processing for a larger geographical region, in order to reduce the number of switches in the network. The telecommunications industry often refers to this as “network flattening” or “network collapsing,” and it can provide many advantages to the network operator, such as lower equipment costs, lower operating and maintenance costs, more efficient use of complex switching software and routing databases, simpler network management, etc.
U.S. application Ser. No. 10/971,821 discloses the use of an emergency standalone switching device. The switching system interface may then be equipped with the emergency standalone switching device, so that the combination can be used with the regional full-featured switching system while maintaining the capability to make local and 911 calls in a serving area that is temporarily isolated from the regional system due to equipment failure, facility damage, or other reasons. This combination also has the advantage that the switching system interface can be used to aggregate subscribers in the serving area that are served through DLCs, as well as those served through legacy line/trunk frames. This allows all subscribers served by time-division multiplexed equipment to be protected by the emergency standalone switching device in the switching system interface, and for call processing to take place through one call control interface to the switching system interface. This simplifies the network topology and simplifies the task of administering the databases necessary for the emergency standalone switching device.
It would also be advantageous to aggregate subscribers who use packet-based telephones, such as IP phones that are now being used by some businesses, or who use telephones connected to packet-based access networks, such as new-generation telephone service over cable systems. This would allow all subscribers in a serving area to be protected by the emergency standalone switching device in the switching system interface, and for all call processing to take place through one call control interface to the switching system interface. This configuration provides the benefit of simplifying the network topology to the point where all forms of telephony would integrate seamlessly into one network.
Therefore, a system and method is needed to implement the conversion between time-division multiplexed digital signals and packetized digital signals within the switching system interface, along with the emergency standalone switching device, in such a way that all subscribers in a serving area can be served by the same call processing interface and the same regional full-featured switching system, and be protected by a common emergency standalone switching device with a common database. In addition, the entire combination should be able to route and process calls between subscribers within a serving area without the need for external switching equipment, such as a softswitch.
Thus, it would be a distinct advantage to provide a system and method to combine a conversion between time-division multiplexed digital signals and packetized digital signals with a switching system interface used to bypass the common control and switch matrix of a class 5 digital switch, and also with a switching system interface that includes an emergency standalone switching device. It is an object of the present invention to provide such a system and method.